Approximately 50 million Americans suffer from ~100 known autoimmune diseases (e.g., type I diabetes, Crohn's disease, and rheumatoid arthritis). The proposed studies focus on the impact of a novel TCR-induced interaction between protein kinase C-theta (PKC?) and CD28 on different aspects of immune responses and its implication for treating autoimmune and inflammatory diseases. PKC? is a Ca2+-independent PKC family member that is most abundantly expressed in T cells, and its critical role in conventional T cell activation and survival has been well documented. In vivo studies revealed the selective role of PKC? in different types of immunity. In particular, a recent study showed that in sharp contrast to T effector (Teff) cells, PKC? is excluded from the immunological synapse (IS) of induced regulatory T (iTreg) cells and, moreover, it inhibits their suppressive function. These findings point to the high promise of PKC? as a selective drug target for immunosuppression of T cell-mediated autoimmunity and inflammation. My preliminary data demonstrated that blocking the PKC?-CD28 association by different strategies promoted the differentiation and suppressive function of Treg cells. Here, I will test the hypothesis that blockade of the PKC?-CD28 interaction inhibits the differentiation and activity of pathogenic T cells and promotes the functin of Treg cells, thereby achieving a beneficial synergetic effect against T cell-mediated autoimmune and inflammatory responses. I will use two novel and highly specific complementary tools, i.e., i) blockade of the inducible PKC?-CD28 interaction by a dominant negative PKC? V3-based mutant; and ii) small molecule allosteric compounds generated by our collaborators that I found to inhibit this interaction. In Aim 1, I will analyze the effect of thes strategies on Teff and Treg differentiation and function in vitro, and in Aim 2, I will evaluate th impact of blocking the PKC?-CD28 interaction on an experimental disease model of chronic colitis in mice. The results of this project will reveal the effects of sequestering PKC? from CD28 and the IS on Treg and Teff differentiation and function and uncover a promising novel approach for treating T cell-mediated experimental inflammatory disease, i.e., Th17-mediated colitis. Collectively, this study is likely to pave the way for the development of new, highly selective therapeutic strategies to treat T cell-mediated autoimmunity and inflammation. This project fits seamlessly with the NIAID mission to conduct and support research to study the causes of allergic, immunologic, and infectious diseases, and to develop better means of preventing, diagnosing, and treating these illnesses. Meanwhile, this project also has close relevance to the mission of the NIDDK as it will study the effects of blocking the PKC?-CD28 interaction on an experimental chronic colitis model.